304 NeduraUPhihsophical Cdhctions. 



which the piece to be tried is brought into contact witli the acid and the wire of 

 the multiplier. The deviation of the needle shows which contains the most alloy, 

 and another trial plate must be employed till the needle cease to be affected, when 

 both are of equal fineness. In coming to a conclusion on this point, however, 

 several circmnstances are to be taken into consideration. Wrought silver goods 

 are generally deprived of a portion of their copper by the action of acids, so as to 

 render the surface finer than the inner part of the metal ; the proof plates, there- 

 fore, must be prepared in the «ame way. Another source of error in the indica- 

 tions of the needle, are the unequal polish and size of the two pieces of metal ; the 

 latter of these is especially difficult to overcome when the surface of the metal to 

 be proved is not plain. When, instead of muriatic acid, a dilute solution of 

 caustic potash is employed, and the result is unlike, it is shown that copper is 

 not the only alloy, but that brass is present ; and the potash solution renders that 

 which contains brass so positive, that it seems considerably purer than the trial 

 plate. This is the case also in a very high degree when the alloyed metal con- 

 tains arsenic, for example when what is called white metal has been used for an 

 alloy. This mode of proof is exceedingly interesting in a scientific point of view, 

 and cases may occur in which it can be employed with advantage ; but the sources 

 of error can scarcely be ever so completely done away with as to make it a prac- 

 tical instrument in the hands of the silversmith, as Oersted seems to expect— /6. 



Iron Pyrites — It is known to mineralogists that common or octohaedral 

 pyrites and the white pyrites, which from their difference of form were considered 

 by Haiiy as different species, were found by Berzelius to be identical in composi. 

 tion, or at least that no such difference existed as to warrant their being con- 

 sidered as difl!erent species. The explanation then given by Berzelius has been 

 confirmed by later experiments, and he has published the following additional 

 remarks : " When a portion of common pyrites was permitted to fall asunder, I 

 found it to be caused by the formation of a small quantity of protosulphate of 

 iron, which burst asunder the crystallized mass. When the salt was dissolved 

 in water no trace of free sulphur was obtained, from which it appeared, that the 

 efflorescing pyrites contains particles of F e S (sulphuret of iron,) which, chang- 

 ing to the state of sdt, tears asunder the rest which undergoes no change. When 

 the small quantity thus changed into sulphate of iron is compared with that 

 which remains unaltered, 1 did not think that the results of analysis could be 

 obtained to such a degree of accuracy as to determine the matter with certainty. 

 I have since obtained a satisfactory proof of the accuracy of this explanation. I 

 heated carbonate of iron gently in a stream of sulphuretted-hydrogen. There 

 were formed first sulphuret, and afterwards bisulphuret of iron. The ex- 

 periment being stopped before all the iron was changed into bisulphuret, a pyrite 

 was obtained, which in a few days fell asunder in all directions, and changed 

 into a woolly mass of vitriol of ten times its former volume. Sesqui-sulphuret of 

 iron prepared from the oxide has not this property. It seems, therefore, highly 

 probable, that the falling asunder of the common pyrites arises from the electro- 

 chemical action of the electro-negative bisulphuret upon the sulphuret which is 

 here and there mixed with it in small particles Ibid. 



Buccina, — a new principle in Box-ivood An apothecary of Bordeaux announ- 

 ced to the Pharmaceutical Society of Paris, at its last sitting, that he had discover- 

 ed in the wood, and particularly in the bark, of the box-tree, an alkaline principle, 

 to which he gives the name of buccina. It is in the form of powder, and neu- 

 tralizes acids, forming uncrystallizable salts : it has a very strong sudorific action 

 and bitter taste. M. Dupetit Thouars, in making this statement at the Philo- 

 mathic Society, remarked that buccina might perhaps be advantageously used in 

 the manufacture of beer, " for there is more box-wood than hops employed in 

 making almost all the beer brewed in Paris." — N. M. Mag. xxx. 112. 



